On-off valve in a fuel injection system for internal combustion engines

ABSTRACT

A fuel injection system has a low-pressure pump for withdrawing fuel from a tank and a high-pressure pump, which is supplied by the low-pressure pump and has camshaft-actuated pump elements. An on-off valve is connected on the inlet side to the pressure side of the low-pressure pump and on the outlet side, is connected on the one hand to a camshaft chamber of the high-pressure pump and on the other hand, is connected to the suction side of the low-pressure pump. At a first pressure threshold, a spring-loaded valve piston of the on-off valve opens a connection between the low-pressure pump and the camshaft chamber and at a relatively higher second pressure threshold, opens a connection between the pressure side and the suction side of the low-pressure pump. A throttle bore in the bottom of the valve piston serves to ventilate the low-pressure system.

CROSS-REFERENCE TO RELATED APPLICATION

This is a 35 USC 371 application of PCT/DE 98/03628 filed on Dec. 10,1998.

BACKGROUND OF THE INVENTION

This invention is directed to an on-off valve and more particularly toan on-off valve especially useful in a fuel injection system for aninternal combustion engine.

DESCRIPTION OF THE PRIOR ART

A known fuel injection system for internal combustion engines is isdisclosed in DE 44 01 074 A1. This system has a low-pressure pump thataspirates fuel from a tank and delivers it to a high-pressure pump. Anon-off valve with a compression spring-loaded sleeve-shaped valve pistonis disposed in the connecting line between the two pumps. This valvepiston has a throttle bore in its bottom, via which the low-pressurepump continuously communicates with a camshaft chamber of thehigh-pressure pump, which is embodied as a radial piston pump. Thecamshaft chamber is in turn connected to the fuel tank.

In this system, the valve piston can be moved by the pressure of thefuel delivered by the low-pressure pump counter to the force of thecompression spring. When a pressure threshold is exceeded, the valvepiston opens a line connection to pump elements of the high-pressurepump.

The on-off valve has several functions: on the one hand, thelow-pressure part of the fuel injection system can be ventilated on theway via the throttle bore and the camshaft chamber. On the other hand,fuel serving as a lubricant is supplied to the camshaft chamber via thethrottle bore. Moreover, in the event of a defect in the high-pressurepart of the system, the on-off valve is intended to function as ashut-off valve in order to protect the engine. With this knownembodiment, however, it is disadvantageous that the fuel flow notwithdrawn by the high-pressure pump results in an uneconomical operationof the low-pressure pump.

SUMMARY OF THE INVENTION

The on-off valve according to the invention, has the advantage over theabove prior art valve that outside the direct line connection betweenthe low-pressure pump and the high-pressure pump, in addition to theventilation of the low-pressure part of the fuel injection system andthe dimensioning of the lubricant flow to camshaft of the high-pressurepump, it also assures that the fuel volume flow not withdrawn by thehigh-pressure pump is diverted directly to the suction side of thelow-pressure pump. In so doing, the on-off valve controls two fuelcircuits, namely the circuit used to lubricate and cool thehigh-pressure pump and the circuit used to return the diverted fuel,wherein the first circuit remains largely uninfluenced when the secondcircuit is switched on. Moreover, the return of the diverted fueldirectly to the suction side of the low-pressure pump increases thedelivery capacity of this pump since a preliminary filter of the systemrequired for filtering the fuel can be bypassed.

The valve of the present invention is advantageous because several valvefunctions can be performed by a single movable valve member. Inaddition, the valve can be completely preassembled and tested as astandard component. Due to its disposition in the housing of thehigh-pressure pump, the installation of the valve into the systeminvolves little expense, in particular, only one seal in relation to theoutside is required since the screw thread hydraulically separates theconnections of the pump housing to the camshaft chamber and the suctionside of the low-pressure pump from each other to a sufficient degree. Asa result, the on-off valve can be produced with a relatively short valvehousing.

BRIEF DESCRIPTION OF THE DRAWINGS

Other advantages of the improved on-off valve will be apparent from thedetailed description contained below, taken with the drawings, in which:

FIG. 1 is a hydraulic connection diagram of a schematically depictedfuel injection system with an on-off valve associated with ahigh-pressure pump and

FIG. 2 is a longitudinal section through the on-off valve.

DESCRIPTION OF THE PREFERRED EMBODIMENT

A fuel accumulator injection system 10 for internal combustion engines,i.e. direct-injecting diesel engines, which is shown in a highlysimplified form in FIG. 1, contains the following essential elements: alow-pressure pump 11, a high-pressure pump 12, a high-pressure fuelaccumulator or common rail 13, injection solenoid valves (injectors) 14,a quantity regulating valve 15, and an on-off valve 16. The low-pressurepump 11 is connected with a suction line 17 to a fuel container or tank18 and with a low-pressure line 19 to the high-pressure pump 12. Thequantity regulating valve 15 is disposed in the low-pressure line 19.The high-pressure pump 12 that is supplied by the low-pressure pump 11is in turn connected on its outlet side by means of a high-pressure line20 with the high-pressure fuel accumulator 13, which is connected to theinjection solenoid valves 14, and a tank outlet line 21 leads fromvalves 14 to the fuel tank 18. The operation of the fuel accumulatorinjection system 10 is known so that the discussion below involves onlythe disposition of the on-off valve 16 in the system, as well as thedesign and function of the on-off valve 16.

The high-pressure pump 12 is embodied in the structural form of a radialpiston pump with a number of pump elements 23, only one of which isshown in FIG. 1. A camshaft 24 (or an eccentric shaft or crankshaft) isused to drive the pump elements 23. The camshaft 24 is disposed in acamshaft chamber 25 of a pump housing 26. From the on-off valve 16,which is connected on the inlet side to the low-pressure line 19, asupply line 27 leads into the camshaft chamber 25 and a return line 28leads to the suction line 17 of the low-pressure pump 11. The camshaftchamber 25 is in turn connected on the outlet side to the tank outletline 21.

The exemplary embodiment of the on-off valve 16 shown in FIG. 2 employsa valve housing 32, which is embodied as a hollow cylindrical screwedpart and is predominantly enclosed in a blind hole bore 31 of the pumphousing 26 of the high-pressure pump 25, and the stepped through bore 33of this valve housing 32 contains a longitudinally movable valve piston34, a helical compression spring 35 disposed in coaxial series with thisvalve piston, and a ball 36 that seals the through bore 33 in apressure-tight manner in relation to the outside. The valve housing 32has an externally threaded section 37 with which it is screwed into theblind hole bore 31 through the engagement of a nut 38 disposed on thevalve housing. In the position of the valve housing 32 shown, its endface 39 disposed at the bottom in the drawing engages with the borebottom 40 of the blind hole bore 31. At the mouth end 41 of the blindhole bore 31, the valve housing 32 is sealed with a sealing ring 42.

Between the sealing ring 42 and the bore bottom 40, the valve housing 32is provided with two transverse bores 45 and 46 that cross the throughbore 33. The transverse bore 45 oriented nearest the sealing ringcommunicates with a first outlet bore 47 of the pump housing 26. Thefirst outlet bore 47 is part of the supply line 27 to the camshaftchamber 25 of the high-pressure pump 12 (see FIG. 1). The secondtransverse bore 46 of the valve housing 32 remote from the sealing ringcommunicates with a second outlet bore 48 of the pump housing 26. Thesecond outlet bore 48 is part of the return line 28 leading to thesuction side of the low-pressure pump 11. At the end of the valvehousing 32, an inlet bore 49 is connected to the through bore 33. Theinlet bore 49 is connected to the low-pressure line 19 leading from thelow-pressure pump 11 to the high-pressure pump 12. Due to the sealedengagement of the valve housing 32 with the bore bottom 40, the secondoutlet bore 48 is completely separated from the inlet bore 49. Asufficient hydraulic seal is produced between the first outlet bore 47and the second outlet bore 48 by means of the screw connection(externally threaded section 37) between the valve housing 32 and thepump housing 26.

The sleeve-shaped valve piston 34 is snugly contained in the throughbore 33 of the valve housing 32. In the rest position of the on-offvalve 16, the valve piston 34 is supported with a snap ring 51 disposedon its circumference against a step 52 of the through bore 33 as aresult of the spring force of the helical compression spring 35 engagingthe valve piston. Its initial tension is adjusted by a correspondinglydeep press-fitting of the ball 36 into the through bore 33. In itspiston bottom 53 oriented toward the spring, the valve piston 34 has athrottle bore 54 which connects the section of the through bore 33oriented toward the spring to the inner chamber 55 of the valve piston34. On the circumference side, the valve piston 34 has an annular groove56 which communicates with the internal chamber 55 by means of one or anumber of throttle bores 57. The annular groove 56 of the valve piston34 constitutes a first control edge 58, which is associated with ahollow, conical first control contour 59 of the valve housing 32 on thestep 52 of the through bore 33. On its end remote from the spring, thevalve piston 54 has a second control edge 60, which cooperates with thetransverse bore 46 of the valve housing 32 that constitutes a secondcontrol contour 61.

In the depicted rest position of the on-off valve 16, the valve piston34 closes the connection from the inlet bore 49 through the throttlebore 57 to the first outlet bore 47 as well as from the inlet bore 49 tothe second outlet bore 48.

The inlet bore 49, however, continuously communicates with the camshaftchamber 25 of the high-pressure pump 12 by means of the throttle bore 54in the piston bottom 53. When the low-pressure pump 11 is started up,air disposed in the low-pressure system can flow out through thethrottle bore 54 in the piston bottom 56 of the valve piston 34, throughthe first outlet bore 47, into the camshaft chamber 25 and from this,can flow out through the tank outlet line 21. This effectively achievesa ventilation of the low-pressure system.

With increasing delivery pressure of the fuel that the low-pressure pump11 withdraws from the tank 18 and supplies to the on-off valve 16 bymeans of the inlet bore 49, the valve piston 34 is moved out of its restposition counter to the spring force of the compression spring 35. Whena first pressure threshold is exceeded, the first control edge 58 of thevalve piston 34 arrives in the vicinity of the control contour 59 sothat a fuel flow can travel from the inlet bore 49, through the throttlebore 57 of the valve piston 34, to the first outlet bore 47, and on intothe camshaft chamber 25 of the high-pressure pump 12. With a smallstroke of the valve piston 34, the on-off valve 16 functions as a flowregulating valve which adjusts a fuel volume flow that is sufficient forlubricating and cooling the high-pressure pump 12. This is supplementedby the partial fuel quantity traveling through the throttle bore 54 inthe piston bottom 53 that extends parallel to the throttle bore 57.

With further increasing delivery pressure of the low-pressure pump 11,when a second pressure threshold is exceeded, which is higher than thefirst pressure threshold, the valve piston 34, which is longitudinallymoved in the direction of the ball 36, unblocks the lateral bore 46 ofthe valve housing 32 with its second control edge 60. Fuel that is notwithdrawn by the high-pressure pump 12 is diverted directly to thesuction side of the low-pressure pump 11 through the second outlet bore48 and the return line 28. The on-off valve 16 now also functions as apressure regulating valve which keeps the inlet side pressure largelyfree of fluctuations. The pressure regulation has an advantageous effecton the quantity regulating valve 15 because having a fuel that is low inpressure fluctuations supplied to this valve supports the functioning ofthe valve.

The foregoing relates to preferred exemplary embodiments of theinvention, it being understood that other variant and embodimentsthereof are possible within the spirit and scope of the invention, thelatter being defined by the appended claims.

We claim:
 1. In an on-off valve (16) for use in a fuel injection system(10) for internal combustion engines, the system housing a low-pressurepump (11) for withdrawing fuel from a tank (18) and a high-pressure pump(12) that is supplied by the low-pressure pump (11) andcamshaft-actuated pump elements (23), wherein the on-off valve (16) hasa sleeve-shaped valve piston (34), which can be longitudinally moved bythe pressure of the low-pressure pump (11) and is loaded by aprestressed helical compression spring (35), has a throttle bore (54) inthe piston bottom (53) and, at a predetermined pressure threshold of thefuel delivered by the low-pressure pump (11), opens an outlet bore (48)in a valve housing (32) that guides the piston (34), wherein thethrottle bore (54), on its outlet side, continuously communicates with achamber (25), which contains the camshaft (24) and belongs to a housing(26) of the high-pressure pump (12), which chamber is connected to thefuel tank (18), the improvement wherein, at a first pressure threshold,the valve piston (34) controls a connection (49, 55, 57, 45, 47)extending parallel to the throttle bore (54), between the low-pressurepump (11) and the camshaft chamber (25) of the high-pressure pump (12),and at a relatively higher second pressure threshold, opens the outletbore (48) which communicates directly with the suction side of thelow-pressure pump (11).
 2. The valve according to claim 1, wherein, whenthe first pressure threshold is exceeded, the valve piston (34), incooperation with a first control contour (59) of the valve housing (32),functions as a flow regulating valve and when the second pressurethreshold is exceeded, the valve piston (34), in cooperation with asecond control contour (61) of the valve housing (32), performs apressure regulating function.
 3. The valve according to claim 2, whereinthe valve housing (32) is contained in the housing (26) of thehigh-pressure pump (12), the valve housing (32) is a hollow, cylindricalscrewed part, the valve piston (34) and the compression spring (35) arecontained in coaxial series in the through bore (33) of the valve,wherein the throttle bore (54) of the piston (34) is disposed orientedtoward the spring, at the end remote from the spring, the through bore(33) is connected to an inlet bore (49) that communicates with thepressure side of the low-pressure pump (11), at the end oriented towardthe spring, the through bore (33) is connected to the camshaft chamber(25) of the high-pressure pump (12) by means of a first transverse bore(45), and at the end remote from the spring, the through bore (33) iscrossed by the second transverse bore (46), which communicates with thesuction side of the low-pressure pump (11) and has the second controlcontour (61).
 4. The valve according to claim 3, wherein, under theprestressing force of the compression spring (35), the valve piston (34)is supported against a step (52) of the through bore (33) of the valvehousing (32) and the prestressing force of the compression spring (35)is adjusted with a ball (36) that is press-fitted into the through bore(33) in a pressure-tight manner.
 5. The valve according to claim 3,wherein the valve housing (32) is disposed in a blind hole bore (31)and, with its end (39) engaging the bottom (40) of the blind hole bore(31), separates the inlet bore (49) from the outlet bore (48) whichcontinues in the pump housing (26), that the valve housing (32) has anexternally threaded section (37), which extends between the firsttransverse bore (45) and the second transverse bore (46) and whichfastens it in the pump housing (26), and that between the firsttransverse bore (45) and the mouth (41) of the blind hole bore (31), thevalve housing (32) is sealed in relation to the pump housing (26) with asealing ring (42).